Yaskawa Reduces Size, Weight of Power Converter by 96%

Yaskawa Electric Corp prototyped an electric power converter that has an output power of 45kW, small size and light weight.

The volume and weight of the new power converter are about 1/25 those of the "A1000," the company's existing product having the same output power. Its dimensions are 35.8 x 28.2 x 2.9cm.

The power converter consists of an AC-DC converter and an inverter (DC-AC conversion). The output power density of the entire power converter is 15kW/L. And the output power density of the inverter is 128kW/L, which is much higher than that of Denso's inverter module that is said to have the industry's highest output power density (60kW/L) as a prototype (See related article).

"Strictly speaking, I do not think it was measured under the same measurement conditions as the one prototyped by our competitor," Yaskawa Electric said. "Still, the output power density of 128kW/L is the highest in the industry."

The small size of the power converter was realized by employing a power module using silicon carbide (SiC)-based power devices and applying driving methods that are suited for the module such as high-speed switching. For example, the switching frequency of the converter is 100kHz while that of the A1000 is about 10kHz. By increasing switching frequency, it became possible to reduce the sizes of passive components, realizing the small size.

This time, Yaskawa Electric used a liquid-cooling method instead of an air-cooling method to reduce the size of the converter's cooling mechanism. If an air-cooling method is used for the converter, its volume will be 1/21 that of the A1000, the company said.

SiC-based power devices supplied by Rohm

The power module and the SiC-based power devices used for the module were manufactured by Rohm Co Ltd. Rohm and Yaskawa Electric have long been co-developing SiC-related devices.

Both the transistors and diodes of the power module use SiC-based power devices. Three SiC-based power devices are used for each of the converter and inverter. The module is a so-called "2-in-1" product, which is equipped with high-side and low-side transistors and diodes for one phase.

The transistor is a "double-trench type" SiC-based MOSFET that is being developed by Rohm. And the diode is a Schottky barrier diode (SBD).

Yaskawa plans to continue the development in the aim of commercializing the power converter using SiC-based power devices by fiscal 2014. And the company expects that it will be used for motors of electric vehicles, driving systems of servomotors, robotic devices, inverter units, etc.

Yaskawa will announce the details of the technologies used for the power converter at the 2012 IEE-Japan Industry Applications Society Conference, which will take place from Aug 21 to 23, 2012, at the Chiba Institute of Technology.